1. Field of the Invention
This invention relates to a display, and a compensation circuit therefor.
2. Description of the Related Art
FIG. 1 illustrates a conventional active matrix organic light-emitting diode (AMOLED) display that includes a display panel 95, a scan line driver 96, and a data line driver 97. The display panel 95 includes an array of pixel circuits 9. The pixel circuits 9 in each row are connected to a scan line 93, whereas the pixel circuits 9 in each column are connected to a data line 94. The scan line driver 96 is connected to the scan lines 93. The data line driver 97 is connected to the data lines 94. Each of the pixel circuits 9, as illustrated in FIG. 2, includes an OLED 91 and a driving member 92. The driving member 92 has a 2T1C structure, and includes first and second transistors 921, 922 and a capacitor 923.
When one of the scan lines 93 is driven by a scan voltage (VSCAN) generated by the scan line driver 96 and one of the data lines 94 is driven by a data voltage (VDATA) generated by the scan line driver 97, the pixel circuit 9, e.g., the pixel circuit 90, on a junction of the scan line 93 and the data line 93 is activated. That is, the first transistor 921 of the pixel circuit 90 is turned on, a capacitor voltage, which corresponds to the data voltage (VDATA), appears across the capacitor 923 of the pixel circuit 90, the second transistor 922 of the pixel circuit 90 is biased into the saturated region by the capacitor voltage and a supply voltage (VDD) and generates a driving current, and the OLED 91 of the pixel circuit 90 is driven by the driving current to emit light. The driving current (IDRIVE) is computed as
      I    DRIVE    =            1      2        ⁢                            k          922                ⁡                  (                                    V                              C                ,                923                                      -                          V                              TH                ,                922                                              )                    2      where k922 is a device trans-conductance parameter of the second transistor 922 of the pixel circuit 90, VC,923 is a capacitor voltage across the capacitor 923 of the pixel circuit 90, and VTH,922 is a threshold voltage of the second transistor 922 of the pixel circuit 90.
The aforementioned conventional AMOLED display is disadvantageous in that, since the threshold voltage of the second transistor 922 differs from one pixel circuit 9 to another due to manufacturing drift and operating conditions, the driving current generated by the second transistor 922 also differs from one pixel circuit 9 to another. As such, the intensities of light emitted by the OLEDs 91 of the pixel circuits 9 are not uniform. In order to minimize the effect of the threshold voltage on the driving current, it has been proposed to add transistors and capacitors to the driving member 92 of each of the pixel circuits 9. This, however, reduces an aperture ratio of the conventional AMOLED display.
Moreover, since the length of a line through which the supply voltage (VDD) is applied increases with the number of the pixel circuits 9, the supply voltage is severely attenuated, particularly for a large size conventional AMOLED display. This also reduces uniformity in the intensities of light emitted by the OLEDs 91 of the conventional AMOLED display.
Furthermore, a voltage across the OLED 91 of each of the pixel circuits 9 of the conventional AMOLED display increases over time. This undesirably affects current flowing through the OLED 91, and thus reduces the light-emitting efficiency of the OLED 91.